Papers by Boris P Toperverg
Physics Letters A, 1978
Abstract Polarization is calculated for magnetic neutron scattering in paramagnetets; it is due t... more Abstract Polarization is calculated for magnetic neutron scattering in paramagnetets; it is due to inteference of the first and the second terms of the perturbation expansion. For critical scattering in ferromagnets this polarization could increase to a measureable value.
Crystallography Reports, 2008
The chromatin organization in chicken erythrocyte nuclei was studied by small-angle neutron scatt... more The chromatin organization in chicken erythrocyte nuclei was studied by small-angle neutron scattering in the scattering-vector range from 1.5 × 10-1 to 10-4 Å-1 with the use of the contrast-variation technique. This scattering-vector range corresponds to linear dimensions from 4 nm to 6 µ m and covers the whole hierarchy of chromatin structures, from the nucleosomal structure to the entire nucleus. The results of the present study allowed the following conclusions to be drawn: (1) both the chromatin-protein structure and the structure of the nucleic acid component in chicken erythrocyte nuclei have mass-fractal properties, (2) the structure of the protein component of chromatin exhibits a fractal behavior on scales extending over two orders of magnitude, from the nucleosomal size to the size of an entire nucleus, and (3) the structure of the nucleic acid component of chromatin in chicken erythrocyte nuclei is likewise of a fractal nature and has two levels of organization or two phases with the crossover point at about 300-400 nm.
Review of Scientific Instruments
M-STAR is a next generation polarized neutron reflectometer with advanced capabilities. A new foc... more M-STAR is a next generation polarized neutron reflectometer with advanced capabilities. A new focusing guide concept is optimized for samples with dimensions down to a millimeter range. A proposed hybrid pulse-skipping chopper will enable experiments at constant geometry at one incident angle in a broad range of wavevector transfer Q up to 0.3 A−1 for specular, off-specular, and GISANS measurements. M-STAR will empower nanoscience and spintronics studies routinely on small samples (∼2 × 2 mm2) and of atomic-scale thickness using versatile experimental conditions of magnetic and/or electric fields, light, and temperature applied in situ to novel complex device-like nanosystems with multiple buried interfaces. M-STAR will enable improved grazing incidence diffraction measurements, as a surface-sensitive depth-resolved probe of, e.g., the out-of-plane component of atomic magnetic moments in ferromagnetic, antiferromagnetic, and more complex structures as well as in-plane atomic-scale s...
Journal of Physics: Condensed Matter, 2018
Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an ... more Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible.
Physica B: Condensed Matter, 1997
Periodic magnetic multilayers Fe/Ge were studied by polarized-neutron reflectometry. The effect o... more Periodic magnetic multilayers Fe/Ge were studied by polarized-neutron reflectometry. The effect of quasi-Bragg enhancement of non-specular diffuse scattering from imperfect interlayer boundaries was observed and explained in terms of neutron diffraction on interfaces with correlated roughnesses.
Physical Review B, 1994
The spin dynamics in the doped antiferromagnetic (AF) state of high-T, copper oxide superconducto... more The spin dynamics in the doped antiferromagnetic (AF) state of high-T, copper oxide superconductors has been investigated within the t-t'-J model. We have shown that a small number of doped holes affects the spin dynamics in the Cu02 planes so strongly that above a very small hole concentration, n, =0. 027, the two-dimensional (2D) AF ground state becomes unstable. We have also predicted a great change in the spin excitation spectrum for the doped AF state. For doping close to n"ahydrodynamic regime of well-deSned magnons collapses, and almost the whole region of long-wavelength spin waves corresponds to the overdamped regime of softened magnons in agreement with inelastic neutronscattering experiments in YBa2Cu306+x reported by Rossat-Mignod et al. Analyzing the imaginary part of the spin susceptibility y"(q, co) we have discovered, in addition to the spin-wave part, also an incoherent band associated with electron-hole excitations. For the overdamped regime the energy ranges of coherent excitations and the incoherent band are overlapped and so it is impossible to separate them. Even for smallest q, when the magnon peak and the band are separated, the relative contribution of the band increases with increasing n and dominates near the critical point.
ABSTRACT Near surface properties of ferro#uid (FF) are studied by means of the neutron re#ectivit... more ABSTRACT Near surface properties of ferro#uid (FF) are studied by means of the neutron re#ectivity and o!-specular scattering measured in zero magnetic "eld, and in a "eld applied within the surface plane, both perpendicular and parallel to the incoming beam direction. It is found that low magnetic "elds substantially perturb the free FF surface which results in dramatic changes in specular re#ection and the o!-specular scattering. This phenomena may be attributed to the "eld-induced anisotropy in the particle density correlation function. The anisotropy is found to be much less pronounced at the interface between FF and the silicon wafer. 2000 Elsevier Science B.V. All rights reserved.
Physica B: Condensed Matter, 1994
ABSTRACT
Physica B: Condensed Matter, 2004
ABSTRACT We report on neutron quantum well states in Fe/Co/Fe trilayers, in which the reflection ... more ABSTRACT We report on neutron quantum well states in Fe/Co/Fe trilayers, in which the reflection potential exhibits a quantum well for both spin states of the neutron. It is shown, that the resonance state in such a system exists and manifests itself as a dip in the reflectivity plateau below the critical angle of total reflection. The range of trilayer parameters was numerically analyzed to find optimal experimental conditions for the enhancement of the neutron wave field in the Co spacer. Enhancement of the wave field by a resonance is suggested as a way to substantially increase the off-specular scattering signal from lateral domains in buried layers of Co.
Applied Physics A: Materials Science & Processing, 2002
We investigate the remagnetization behaviour of remanent polarizing supermirrors by polarized neu... more We investigate the remagnetization behaviour of remanent polarizing supermirrors by polarized neutron reflectometry. Such a mirror can be remagnetized in a magnetic field of 30 mT. It is shown, that at lower fields, the mirror is not completely remagnetized, but the magnetization of the thinner layers can be flipped more easily than the magnetization of the thicker layers. With polarized neutron reflectometry, we are able to find out exactly how many layers are magnetized parallel and how many are magnetized antiparallel to the external field. Furthermore, information about structural and magnetic imperfections (roughness, domain formation) is available.
Langmuir, 2003
For the design of multicompositional materials with a spatially defined order of different compon... more For the design of multicompositional materials with a spatially defined order of different components symmetric polystyrene(deuterated)-block-polybuthyl methacrylate P(Sd-b-BMA) lamellar thin films are used as a structure-directing matrix for the nanoparticle arrangement. A P(Sd-b-BMA) diblock-copolymer film spontaneously self-assembles upon annealing into a lamellar multilayer and orders the PS-coated nanoparticles, incorporated into the polymer solution prior to annealing, in a periodic lamellar structure. Specular reflection and off-specular neutron scattering were applied to determine the distribution of magnetite Fe3O4 nanoparticles in a symmetric P(Sd-b-BMA) film with a concentration of the nanoparticles of 7% of the volume fraction. From the experiments on neutron specular reflection and off-specular scattering, we obtained information about the distribution of the nanoparticles within the lamellae and about the distortion of the lamellar order of the copolymer matrix.
Solid State Communications, 1988
ABSTRACT
Solid State Communications, 1981
... 6 7/ It is easy to show that the polari-zed neutron magnetic ... Let H, PO and q lie in a pla... more ... 6 7/ It is easy to show that the polari-zed neutron magnetic ... Let H, PO and q lie in a plane, and To is parallel or opposite to H. Then in reference frame of Fig.1 we have ( h)( Po) = eX hX Pox + ey by Poy + + e,, e, (hXPo; + ha %x) (4) where h = HH 1. The sign of this expression ...
Physical Review B, 2006
We have investigated the magnetization arrangement in an in-plane stripe pattern with alternating... more We have investigated the magnetization arrangement in an in-plane stripe pattern with alternating exchangebias domains. The stripe pattern was produced by ion bombardment induced magnetic patterning, which changed locally the exchange-bias direction at the ferromagnet/antiferromagnet interface, but not the magnetic or antiferromagnetic properties of the Co 70 Fe 30 and Mn 83 Ir 17 layers, respectively. For the analysis of the magnetic domain structure evolution along the hysteresis loop we used a combination of experimental techniques: magneto-optical Kerr effect, Kerr microscopy, polarized neutron reflectometry, and off-specular scattering of polarized neutrons with polarization analysis. Instead of a perfect antiparallel alignment we found that the magnetization in neighboring stripes is periodically canted with respect to the stripe axis so that the net magnetization of the ferromagnetic film turns almost perpendicular to the stripes. At the same time the projection of the magnetization vector onto the stripe axis has a periodically alternating sign. The experimental observations are explained and quantitatively described within the frame of a phenomenological model, taking into account interfacial exchange bias, intralayer exchange energy, and uniaxial anisotropy. The model defines conditions which can be used for tailoring nano-and micro-patterned exchange-bias systems with different types of magnetic order.
Physical Review B, 2012
We have investigated asymmetric Fe/Cr/Co/Cr superlattices with two magnetic layers of Fe and Co, ... more We have investigated asymmetric Fe/Cr/Co/Cr superlattices with two magnetic layers of Fe and Co, which are different with respect to their magnetic properties: magnetization, coercivity, and magnetic anisotropy. The magnetic layers are weakly coupled via a mediating Cr spacer layer providing an antiferromagnetic alignment of adjacent layers. The magnetic structure of these spin-valve-like Fe/Cr/Co/Cr superlattices was analyzed from the remanent state up to saturation via polarized neutron scattering and polarized neutron reflectivity (PNR). Furthermore, the domain structure in remanence was imaged via polarized x-ray photoemission electron microscopy (XPEEM). This analysis reveals that the Co magnetization strongly affects the Fe domain structure, while the layer magnetization is collinear from the remanent antiparallel state up to the ferromagnetic saturation state. However, for certain Co layer thicknesses, the as-grown remanent state exhibits a noncollinear antiferromagnetic spin structure, which cannot be recovered after applying a magnetic field. However, the noncollinear structure is reproducible with freshly grown superlattices.
Physical Review B, 2008
We present an investigation of the structural and magnetic correlations during the remagnetizatio... more We present an investigation of the structural and magnetic correlations during the remagnetization process of a gradient nanocrystalline multilayer with uniform uniaxial magnetic anisotropy by specular reflectometry and off-specular scattering of polarized neutrons with polarization analysis. The scattering data were analyzed within the distorted wave Born approximation ͑DWBA͒ including interfacial roughness correlations and lateral correlations of the spin misalignment. The magnetization reversal proceeds sequentially from the bottommost and thinnest ferromagnetic layers to the topmost and thickest ones. It is quantitatively explained within the random anisotropy model including dominant uniform uniaxial anisotropy. Two types of lateral spin misalignment were deduced, random and not random: The first one in all layers due to the random orientation of the grains, the second one in the layers with nonreversed magnetizations only and due to the applied field acting against the uniaxial anisotropy.
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Papers by Boris P Toperverg